Preparation of organolead compounds



bon atoms.

United States Patent D f 31.77 130 PREPARATION OF. OIkGA iNOLEAD CGMPGUND Albert P. thliraitis, Baton Rouge, La., assignor to Ethyl Corporation, New York, N .Y., a corporation of Virginia No Drawing. FiledAug. 22, 1962, Ser. No. 218,495 3 Claims. (Cl. 2tl45) This invention relates to the preparation of organolead compounds, especially tetraalkyllead compounds.

Many, methods are known for the production of organolead compounds, especially the tetraalkyllead compounds. The present commercial process for producing tetraethyllead involves the reaction-of a sodium-lead alloy with ethyl chloride. This process suifers certain disadvantages among which is the actual low conversion of the lead to tetraorganolead compound. As a result, attempts have been made to devise other techniques for producing organolead compounds, including electrolytic procedures, but because of certain inherent disadvantages such, procedures have not been commercialized. Therefore, it is still desirable to provide other and more effective methods for the production of organolead compounds, especially the tetraalkyllead compounds.

Accordingly, an object of this invention is to provide a new andnovel process for the production of organolead compounds, particularly the tetraalkyllead compounds. Another object is to provide such compounds in high yield and purity by a more efficient and more economical process. A still further object is to provide a technique for the production of tetraethyllead. These and other objects of the invention will be evident as the discussion sodium methylate, sodium ethylate, and lithium phenate,

and a trihydrocarbon aluminum compound to a cathode. The preferred complexes employed as electrolytes are those of an alkali metal alcoholate of an alkanol having between 1 to 6 carbon atoms and a trialkylaluminum compound wherein the alkyl groups have between 1 to 6 car- Such complexes wherein the alkali metal is sodium or potassium are especially preferred because of their greater availability, higher conductivity, and more elfective results obtained. lnthis regard, sodium or potassium triethylaluminum methylate, ethylate, butylate, and phenate comprise especially preferred embodiments.

The present process is of particular advantage in that it provides a novel method for the production of organolead compounds in a more efficient and economical manner. The electrolytes employed are more readily prepared and of greater stability and easier to handle than are the previously known electrolytes. Further, they result in by-products formed, e.g., dialkylaluminum alkoxides, which although soluble in the organolead product are more easily separated therefrom than are the byproducts'obtained by the use of other previously known electrolytes. Other advantages of the process of this invention will be evident as the discussion proceeds.

The alkali metal alcoholates, otherwise known as alkoxides, used in forming the electrolyte complexes of this invention are subject toconsiderable latitude. The alkali metals are intended to include those metals of Group I-A of the Periodic Chart'of the Elements, e.g., lithium,

sodium, potassium, rubidium, and cesium, with sodium and potassium being particaularly preferred. The term alcoholate is intended to include the salts obtained from 3,177,136 Patented Apr. 6, 1965 an alcohol by replacing the hydroxyl' hydrogen with an alkali metal. Thus, the term includes, for example, alkali metal salts of alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, and aryl alcohols, including combinations of such aliphatic, cycloaliphatic, and aromatic radicals- While the alcoholate can be an alkali metal salt of a polyhydric alcohol, it is preferably one of a monohydric alcohol. Primary, secondary, and tertiary alcohols are employable with the primary alcohols being preferred. Thus, typical examples of the alkali metal alcoholates employed in forming the electrolytes of this inventioninclude sodium methylate, sodium ethylate, sodium butylate, sodium octylate, sodium decylate, sodium octadecylate, and the corresponding potassium, lithium, rubidium, and cesium alcoholates; sodium allylate, sodium decenylate, sodium-S-hexynylate, sodium cyclopentanylate, sodium cyclohexanylate, sodium cyclohexenylate, sodium phenate, sodium benzylate, sodium cresylate, and the like, and the corresponding alcoholates of lithium, potassium, rubidium, and cesium. While the chain lengths of such alcoholates can be as high as 30 or more carbon atoms, generally they will contain preferably up to and including 18 carbons atoms. It is to be understood that the hydrocarbon portion of such alcoholates can be substituted with other organic substitutents, particularly those which are non-reactive with trihydrocarbon aluminum compounds. The alcoholates formed from alkanols are particularly preferred, especially those wherein' the alkyl groups have from 1 to 6 carbon atoms. Thesodium and potassium salts of such alkanols are likewise particularly preferred since the complexes formed therefrom exhibit more useful properties.

Similarly, the trihydrocarbon aluminum compounds employed in forming the electrolyte complexes of the present invention are also subject'to considerable latitude. Such compounds can be, for example, aliphatic, cycloaliphatic, and aromatic aluminum compounds including, for example, trialkyl, trialykenyl, trialkynyl, tricycloalkyl, tricycloalkenyl, and triaryl aluminum compoundsand trihydrocarbon aluminum compounds containing mixtures of such radicals. By way of illustration of the trihydrocarbon aluminum compounds employable, the following are typical examples: trimethylaluminum, triethylalumium, triisobutylaluminum, trihexylaluminum, trioc-tylaluminum, tridecylaluminum, trioctadecylaluminum, tri-S- hexeneylaluminum, tri-S-hexynylaluminum, tricyclohexylaluminum, tricyclohexenylaluminum, triphenylaluminum, tribenzylaluminum, trinaphthylaluminum, ethyl dimethyl aluminum, and the like. Again, while trihydrocarbon alu-' minum compounds of the type exemplified above are preferred, it is to be understood that the hydrocarbon portions can be further substituted, particularly with organic sub stitutents. Here also the chain lengths of'the groups can be as high as 30 carbon atoms and higher, but generally contain up to and including 18 carbon atoms. Of thetrihydrocarbonaluminum compounds, the trialkylaluminum compounds, particularly those wherein the alkyl groups contain between about 1 to 6 carbon atoms are preferred since such are more readily available and of greater utility.

In this regard, triethylaluminum comprises an especially.

preferred embodiment.

The novel electrolyte complexes of the present invention are obtained preferably by mixing an alkali metalalcoholate, such as those typified above, in essentiallyanhydrous and alcohol-free condition with a trihydrocarbon aluminum compound, preferably with heating in the presence of an inert atmosphere such as nitrogen. The proportion of the alcoholate to the trihydrocarbon aluminum compound can be varied slightly although complex formation wherein essentially one mole of the alkali metal alcoholate and one mole of the trihydrocarbon aluminum compound are employed is preferred and such are readily prepared by heating a mixture of the two compounds, it

necessary, to provide one of the reactants in the liquid state. Alternatively, a suitable inert organic solvent, such as the hydrocarbons or ethers, can be employed to sol-.

ubiliz'e one of the ingredients, v:especially the trihydrocarbon aluminum compound and thenheating asrequired, to accelerate formation of the complex. Thus, such electrolyte complexes are alternatively described as alkali metal trihydrocarbon aluminum alcoholates having the typical structural formula wherein R and R can be the same or different, preferably hydrocarbon groups as illustrated above in connection with the alkali metal alcoholates and the trihydrocarbon.

ethylaluminum phenate, sodium trioctylaluminumethyl ate, sodium trihexylaluminum octylate, sodium triphenylaluminum hexylate, sodium triphenylaluminum decylate,

' sodium tricyclohexylaluminum, butylate, sodium triisopropylaluminum methylate, sodium triphenylaluminum methylate, and the corresponding complexes of other as .well as other equimolar combinations of the hereinbefore described alkali metal alcoholates and trihydrocarbon aluminum compounds.

The present invention is further illustrated by the following examples wherein all'parts are by weight unless otherwise specified.

Example I An electrolytic cell is provided having a lead anode and a copper cathode. To the cell is added an equimolar mixture of sodium ethylate, essentially alcohol-free, and tri ethylaluminum; The cell is heated to about 105 C. whereby all the sodium ethylate reacts'forming the'liquid equimolar complex, sodium triethylaluminum ethylate. The cell is then maintained at this temperature for the remainder of the operation. The cell is then operated at lead mixture can be distilled, preferably under reduced.

pressure, to effect separation and thus permit reuse of the diethylaluminum ethylate in regenerating the electrolyte.

Example II Employing the procedure of Example 1, sodium triethylaluminum butylate is used as the electrolyte and the cell continuously operated at 95 C. at a current density of 4.milliamps/cm. The tetraethyllead is continuously withdrawn in admixture with the diethylaluminum butylate and the former separated therefrom by distillation under vacuum. a V

Example Ill The procedure of Example I is 'r'epeatedwith the exception that lithium triethylaluminum 'phenate is employed as the electrolyte with an operating temperature of 125 C.

' and a current density of l milliamp/mfi.

lead, is produced.

Tetraethylalkali metals, especially potassium, and mixturesthereof,

Simultaneously,

, Example I V a When Example I is repeated substituting potassium tributylaluminurn butylate as the principal component of the electrolyte, operating at :a current density of 2 milliamps/cm. and a temperature of 90 C., tetrabutyllead is obtained at a high current efficiency.

Example .V

Example I is repeated substituting sodium trimethylaluminum ethylate as the electrolyte. Tetramethyllead is produced in essentially a quantitative current efficiency along with dimethylaluminum ethylate andsodium. The dimethylaluminum ethylate is *readilyseparated from the tetramethyllead by fractional distillatiom To illustrate the process carried out in conjunction with an electrolyte regeneration. step, for complete integrated process, the following example is illustrative.

Exam ple A cell containing a copper cathode and a lead anode is charged with sodium triethyl aluminum ethylate, as in Example I. Electrolysis is carried out at a temperature.

The anode product is a liquid mixture oftetraethyllead and aluminum'diethyl ethylate, having about 38 weight percent tetraethyllead. The mixture is separated by a vapor stripping operation,- using nitrogenas an inertgas stripping agent and carrying out the vaporization at a pressure-of about one-tenth atmosphere and a temperature of 50-.-60 C; The; tetraethyllead is condensed from the overhead gas phase and is immediately blended with other agents for product mixtures. f The sodium metal released at the cathode is also continu'o usly withdrawn and is then treated with hydrogen gas, under agitation conditions, to convert the sodium to sodium hydride. The granular or powdered sodium hydride is then admixed with the aluminum diethyl ethoxide obtained from the separation of anode products. The resultant complex is then subjected to'ethylenepressure, to regenerate sodium aluminum triethyl ethoxide, which is returned to the. electrolysis cell topreserve steady state conditions. g

The above examples have been presented by Way of illustration of theprocess of this invention and it is not intended to be limited thereto. Itwill now be'evident that other complexes described hereinbefore can be-substituted to formother organolead products.

There are many other modes of preparation of the complex elecetrolytes available, among which are included, for example, the reaction of thecorresponding.

alkali metal tetraorganoaluminum compound with the appropriate alcohol, e.g., the reaction of. sodiumtetraethyhs metalwith hydrogen to form the hydride by known techniques, thenreaet the hydridewith the recovered .dihy- 'drocarbon' aluminum.alcoholate to'form the correspond-v methods for the preparation 'of' the electrolytecomplexes.

will now be evident.

The temperature'during electrolysis is not critical. It

should be sufliciently high to provide a liquid electrolyte with reasonable. conductivity but should not be appreciably above the decomposition temperature of the electrolyte or the organolead products. Thus, thegoperating' temperature of thereaction depends upon the particular electrolytes and products involved. In general, suitable temperatures are between about 0 and about 120 C., but temperatures from about 80 to 110 C. are preferred for maximum current efiiciency, conductivity, and best results. Suitable results are obtained in the above examples at temperatures of 80, 90, and 110 C. Know stabilizing materials are desirably provided to protect the organolead material from thermal decomposition at the conditions of electrolysis, or during recovery. Typical examples of such stabilizers are alkyl-substituted aromatic hydrocarbons, such as toluene and xylene; condensed aromatic hydrocarbons, such as naphthelene; and conjugated dienes.

Atmospheric pressure is normally employed. While subsatmospheric pressures are permissible, the affinity of the reactants for moisture and oxygen usually makes the operation hazardous and impractical. A mild pressure of inert gas is sometimes desirable, for example, to assure anhydrous conditions.

In some instances various diluents can be employed during the electrolysis step. The principal requirement for the diluent is that it dissolve in the electrolyte. The use of a diluent, however, is not essential to the operation of the process and its absence may be desirable in some instances. en employed, hydrocarbons such as toluene are well suited.

The lead anode can be pure lead or alloys thereof of Typical examples of alloy metals are varying shapes. tin, bismuth, cadmium, antimony and copper. In some cases sodium, lithium, magnesium, and zinc are suitable.

The cathode can be any suitable conductive metal such about 2 and 50 volts, although not greater than 20 volts is normally required or desirable. Preferably, a potential of 4-15 volts is employed. The conversion of lead is es- 1 sentially 100 percent of theory. In general, not greater than 0.25 ampere/cm. is employed. A preferred range is between 0.001 to 0.1 ampere/0m process. Generally, of course, the electrodes should be spaced as closely as feasible to lower the voltage requirements for specific current flow. As the cathode and anode products are normally liquid at the preferred conditions of operation, collection sumps facilitate collection and withdrawal from the cell.

While the above examples have illustrated the use of the alkali trihydrocarbon alcoholate complexes as the principal component of the electrolyte, it is to be understood that they can be employed as components of other electrolytes to still achieve the advantages of this invention, improve conductivity, and lower the melting point. By way of example, an electrolyte comprising a mixture of an alkali metal trihydrocarbon aluminum alcoholate complex and an alkali metal tetraalkylaluminum compound can be used.

This application is a continuation-in-part of my copending application, Ser. No. 41,786, filed July 11, 1960, now abandoned, which was a continuation-in-part of my application Ser. No. 563,422, filed February 6, 1956 and now Patent 2,944,948.

Having thus described the novel process of this inven tion, it is not intended that it be limited except as set forth in the following claims.

I claim:

1. A process for the manufacture of a tetrahydrocarbon lead comprising passing an electric current through an electrolyte in an electrolysis zone, and through a lead containing anode in contact with the electrolyte, said electrolyte comprising an alkali metal trihydrocarbon aluminum alcoholate, forming thereby a tetrahydrocarbon lead at the anode and then withdrawing the tetrahydrocarbon lead from said zone.

2. A process for the manufacture of tetraethyllead comprising passing an electric current through an electrolyte in an electrolysis zone, and through a lead containing anode in contact with the electrolyte, said electrolyte comprising sodium triethyl aluminum ethylate maintained at a temperature of about 105 C., and forming thereby tetraethyllead at the anode, and then withdrawing the tetraethyllead from said zone.

3. The process of claim 1 wherein the electrolyte comprises an alkali metal trialkylaluminum alcoholate. The electrolytic 5, cells employed can assume a variety of forms, and specific construction is not critical to the efiiciency of the Y References Cited by the Examiner UNITED STATES PATENTS 3,088,885 5/63 McKay 204-59 JOHN H. MACK, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,177,150 April 6, 1965 Albert P. Giraitis It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 74, for "Inilliamp/m. read millisunp/cm. column 5, line l5, for "subsatmospheric" read subatmospheric Signed and sealed this 21st day of September 1965.

(SEAL) Allest:

EDWARD J. BRENNER 

1. A PROCESS FOR THE MANUFACTURE OF A TETRAHYDROCARBON LEAD COMPRISING PASSING AN ELECTRIC CURRENT THROUGH AN ELECTROLYTE IN AN ELECTROLYSIS ZONE, AND THROUGH A LEAD CONTAINING ANODE IN CONTACT WITH THE ELECTROLYTE, SAID ELECTROLYTE COMPRISING AN ALKALI METAL TRIHYDROCARBON ALUMINUM ALCOHOLATE, FORMING THEREBY A TETRAHYDROCARBON LEAD AT THE ANODE AND THEN WITHDRAWING THE TETRAHYDROCARBON LEAD FROM SAID ZONE. 